Ion implanters are widely used in semiconductor manufacturing to selectively alter the conductivity of various electronic materials. In a typical ion implanter, ions generated from an ion source are directed through a series of beam-line components which include one or more analyzing magnets and a plurality of electrodes. The analyzing magnets select the desired ion species, filter out contaminant species and energies, and adjust the beam quality at the wafer. The electrodes modify the energy and shape of the ion beam.
FIG. 1 shows a known ion implanter 100 which comprises an ion source 102, extraction electrodes 104, a 90° magnet analyzer 106, a first deceleration (D1) stage 108, a 70° magnet 110, and a second deceleration (D2) stage 112. The D1 and D2 deceleration stages (also known as “deceleration lenses”) are each comprised of multiple electrodes with a defined aperture to allow ions to pass therethrough. By applying different combinations of voltage potentials to the D1 and D2 deceleration stages, the ion implanter 100 may operate in different modes. For example, in a process chamber deceleration (PCD) mode, no voltage potential is applied to the D1 electrodes, such that the ion beam drifts until it reaches the D2 electrodes. In a double deceleration (DD) mode, however, deceleration potentials are applied to both D1 and D2 electrodes, so that the ions are decelerated at both stages.
Traditional ion implanters are ill-fitted to varying modes of beam operation. When an ion implanter is switched from one operation mode to another, there may be a significant change in the ion beam geometry. For example, in the ion implanter 100 illustrated in FIG. 1, a ribbon-shaped ion beam that has been decelerated at the D1 stage typically has a current density distribution that is significantly taller than a beam that has not been decelerated at the D1 stage. That is, the ion beam tends to be taller when it reaches the D2 stage if the ion implanter 100 is operating in DD mode than if it is operating in PCD mode. In traditional ion implanters, the D2 deceleration lens typically has a fixed aperture that is just wide enough to accommodate the vertical height of the ion beam in DD mode. However, in PCD mode, the aspect ratio of the fixed aperture provides poor or no vertical focusing of the shorter ion beam, which often leads to an excessive beam height as well as difficulties in uniformity tuning.
In view of the foregoing, it would be desirable to provide a solution which overcomes the above-described inadequacies and shortcomings.